Trading hours of US stocks
How to place an order
Other limits for placing US stocks orders
How to modify/cancel an order
Whether use the pre and post-market price to calculate the market value and profit or loss of your position
Why should the placement of market orders be restricted
Withholding Tax on Publicly Traded Partnerships (PTP) Securities and Trading Arrangements
Market orders are executed at uncertain real-time prices. When liquidity is insufficient and transactions are extremely inactive, sharp price fluctuations are prone to occur. You may therefore trade at a price much higher than the current bid price, or much lower than the current ask price and make losses.
You intend to buy the AAPL, but there is no pending sell order in the market. If there are no restrictions on the placement of market orders, your market order may be executed at any price. If the transaction price of your purchase is much higher than the best bid price at that time, you may face greater losses.